1. Field of the Invention
This invention relates to the treatment of oil wells and more particularly to the removal of viscous crude oil, waxes, asphaltenes and resins of petroleum origin from wells, flow lines and the pore spaces in oil-bearing formations.
2. Description of the Prior Art
In the production of petroleum oil and/or gas from a subterranean formation through a well bore leading to the surface of the earth, difficulty is often encountered due to the accumulation of heavy hydrocarbon deposits in flow passages within the well, but more particularly within the pore spaces of the oil-bearing formation itself. The accumulation of heavy hydrocarbons such as waxes, asphaltenes and resin precipitates of petroleum origin ultimately can result in plugging. These accumulations of heavy hydrocarbons are solid or semi-solid at the conditions existing within the well and oil-bearing formation and can reduce the size of the passageways through which the oil or gas must flow. Eventually, with continued production, the well flow passages and the pores of the oil-bearing formation become plugged or restricted. In aggravated cases, accumulation of these heavy hydrocarbons can occur to the extent that the fluid flow to the well, or within the well flow passages, is completely restricted.
A variety of procedures to remove these accumulations of heavy hydrocarbons involving contacting the accumulations with solvents for heavy hydrocarbons are known in the art. Generally, expensive aromatic solvents like toluene, benzene, xylene and hydrocarbon distillates having high aromatic contents, or mixtures of these aromatic compounds with diesel or crude oil are employed. These conventional solvent compositions are usually applied with pressure and in some cases require preheating prior to injection into the well. One drawback in prior art solvent treatments is the rapid swelling of the heavy hydrocarbon deposits in the pores of the formation when contacted with conventional solvent compositions. It is a well known phenomenon that solids when contacted with solvent must swell before they can dissolve. The resulting swelled deposits aggravate the plugging condition by more completely filling the pore spaces. Any further solvent injection is useless unless sufficient pressure is available to overcome this plugging. Even then, the tendency of the injected solvent composition is to finger through the largest channel network in the formation which offers the least resistance and to displace these accumulations of viscous crude oil, waxes, asphaltenes and resin precipitates further away from the well, where they may be in time dissolved and/or dispersed. However, such finger channels may represent only a small fraction of the total channel network of the formation. In most cases, this gives satisfactory results for a short duration but upon return of the well to production these finger channels become rapidly plugged again.
In addition to the above described plugging problem, all oil-bearing sand formations contain interstitial water in the form of a continuous channel network. This thin film of water, which is generally immiscible with conventional solvents, further retards the action of the solvents in dissolving the heavy hydrocarbons. There exists a need in the oil recovery art for economical and effective solvent compositions useful for removing heavy hydrocarbon accumulations which avoid the disadvantages and drawbacks associated with the prior known methods and solvent compositions for treating oil wells.